1. Field of the Invention
The present invention relates to a belt unit of an electrophotographic printing apparatus.
2. Background Art
Here will be described a belt unit, especially a belt photoconductor unit in an electrophotographic printing apparatus according to the related art.
As a general configuration of a belt photoconductor unit, there is known a configuration in which a drive roller for rotating a belt photoconductor and a tension roller having tension urged by springs or the like are provided between two frames for supporting the rollers and in which the belt photoconductor is wound around the rollers.
The belt photoconductor unit is configured so that a sensor for detecting a widthwise end of the belt photoconductor is provided on one of the frames or the like in order to perform detection of misalignment during rotation, detection of a seam of the belt photoconductor, and so on.
The belt photoconductor needs to be exchanged for a new one periodically since it is an expendable article. At the time of exchange, it is necessary to remove the belt photoconductor from the frames and mount a new one. In the related art, it was necessary to shift the tension roller in a direction of narrowing the distance between the drive roller and the tension roller before removal/mounting of the belt photoconductor.
Further, at the time of mounting of the belt photoconductor, the belt photoconductor must be mounted so as to be positioned in a groove of the sensor properly. This work was very difficult. As a related-art technique for setting the belt photoconductor in a proper position, there is known a technique in which: a first cam and a second cam for moving the tension roller in a direction of relaxing the belt photoconductor are provided on opposite ends of a rotating shaft; the length of the first cam is set to be larger than the length of the second cam; slowly increasing tension is applied to the belt photoconductor to thereby mount the belt photoconductor in the groove of the hole sensor (e.g., see JP-A-5-019667 (page 3 and FIG. 3)).
According to the related art, it was structurally difficult to make the length difference between the first and second cams extremely large. For this reason, when a belt photoconductor having a large circumferential length was used, there was the possibility that the belt photoconductor would be scratched so as to be disabled from being used because slackness of the belt photoconductor could not be eliminated reliably to make it impossible to mount the belt photoconductor in the groove of the sensor accurately.
Furthermore, the mounting position of the belt photoconductor was indefinite in the widthwise direction. For this reason, there was the possibility that the belt photoconductor could not exhibit its original performance because the belt photoconductor might be mounted in a position different from the original position where the belt photoconductor should be used. In addition, there was the possibility that the belt photoconductor would be damaged so as to be disabled from being used because the belt photoconductor might come into contact with the sensor.
There was possibility that the belt photoconductor might be inserted into the electrophotographic printing apparatus body while the cams were not restored to their positions at the time of actual printing, that is, to the positions where tension would be applied to the belt photoconductor after the belt photoconductor was mounted. For this reason, there was the possibility that the belt photoconductor was scratched so as to be disabled from being used.